Composite drill collar



` Sept. 7, 1943. A L sTNE L 2,328,856 l COMPOSITE DRILL COLLAR Filed March 2o, 1940 :Bmsgamz A ,l PatentedS'ept. 7, 1943 COMPOSITE DRILL COLLAR Albert L. Stone, Palos Verdes Estates, Calif., as-

sgnor to Hydril Company, Los Angeles, Calif., a corporation of Nevada Application March 20, 1940, Serial No. 325,013

v t 5 Claims. (Cl. Z55- 28) This inventionrelates generally'to drill collars for well-drilling strings and is more particularly concernedwlth an economically manufactured.` composite drill collar which will havea number oiv points. of advantage over those now commonly in use.

is well known, drill collars are heavyvsections of pipe arranged immediately above a drilling tool whereby requisite drilling weight maybe imposed directly onl thevtool, the weight of theA rdrill stem, proper, being taken, in the main,.at the ground surface by the draw works or rotary table. Ideally, the bottom joint of drill pipe im- 4 medlately above the drill collar should be supported inV tension. The reasons for establishingv and maintaining these conditions are well known to those familiar with the art.

, l Drill collars, togivc ,them sufficient weightto serve their purpose, .are necessarily thick-walled and it is important that' their-bores be as nearly 'as possible' concentric withtheir outer faces in order that the rcollars may be `dynamically bal-v anced. Furthermore, the collars must be made so as tov avoid concentration ofbending stresses v and gyrational forces on'rela'tively weak sections. These requirements have resulted `in excessive "costs and manufacturing diiiiculties, and it is therefore an object of my invention is' to provide a v drill collar having proper weight and balance and loadedlstributing characteristics and yet which isproducible'in a manner to reduce-sharply the cost of manufacture. p

How the above advantageous conditions are brought about, as well as other objects and features of novelty oi*` the invention, will be made apparent in the following detailed description, reference being had to the accompanying drawing, in which:

Fig. 1 is an elevation showing my improved drill collar in connection With a usual drilling string;

Fig. 2 is an'enlarged scale, longitudinally contracted section on line 2 2 of Fig. 1, but with the lower tool-joint pin member removed;

Fig. 3 is an enlarged section on line 3-3 of Fig. 2;

Fig. 4 is a schematic view showing one step in the method of producing the drill collar;

Fig. 5 is a transverse section through a nished drill collar showing, in exaggerated form, certain conditions which may prevail;

Fig. 6 is a fragmentary detail showing a variational formi of composite collar; and

Fig. 7 is a fragmentary detail showing another variation.

In Fig. l I have illustrated a fragment of a drilling stem I0 consisting of a usual drill pipe 'II, cutter I 2 and a drill collar I3 intermediate the two. The collar` is here shown as made up of `two sections I4 and Ida detachably connected by a coupling or sub I5. However, it will be understood that the number of sections, whether one, two or more, depends upon the particular circumstances of any given drilling operationv and thereforethe instant showing of two sections is not to be considered as limitative. The several sections may be identical in construction, and I will therefore need to describe onlyone in detail.

Though this is not at all limitative, drill pipe I'I is shown as being of the integral-boxtype, the internally threaded box I 6 being formed in the upset end Il of the pipe. The effective bore I8 of the box is of slightly restricted diameter as compared with themajor bore I9 of the pipe, proper.

While any suitable form of coupling may be utilized for detachably connecting` the drill collar to pipe I I, I have here shown a tool-joint doubleended pin member 20, the body portion of the member being approximately the same outsidel diameter as that of upset I1 and bores I8 and 22 being of approximately the same diameter.

4The pin portions 23 and 24 of member are identical, being provided with threads 25 adapted tomate at one end with the threads in box I8 and at the other end with threads in collar4 section I4, as will be described. The threads are preferably, though not at all necessarily, of the quick make-and-break type, here being shown as relatively coarse and of relatively Vsteep taper.

Coupling member I5 may be of identically thev same Construction as member 20 and therefore the description of-one will'suflice for the other.

Now, drill collar section `I,4"( and, of course, if only one section is used, it may be considered the drill collar, proper) v is composite innature, being made up of inner and 'outer nested, tubular members 25V and 2.6, respectively. The outer member"26 is preferably, though not necessarily, made of drill-stem stock, such as carbon steel with some manganese content, usually heattreated, adapted to take the extremely severe tensile and torsional stresses incident to drilling operations. While the outer member may be of stock originally in the form of rolled steel tubing of uniform thickness throughout its length with threads later formed in its opposite ends, externally flush, internally upset drill pipe is particularly well suited to the instant purpose and I boxes 28 to take, for instance, the threaded pins 23 or 24 of coupling members i5 or 20. The upsets eachhave a bore 29 of approximately the ysame diameter as bores I8 and 22, and the two upsets present opposed annular shoulders 30 spaced apart by the distance between boxes.

Generally, .it may be assumed that any tubing of the ,length requisite for drill-collar sections will not be thick enough to have the weight requisite for drill-collar purposes. It is extremely difcult to drill bores from the opposite ends of solid stock and yet maintain variances of rwall thickness within the allowable limit.

I accomplish the end of giving requisite Weight to the drill collar and yet cheaply and simply insuring a bore which is smooth, uninterrupted and concentric with the outer peripheral face of the collar (thus insuring equal wall thickness throughout) by lining the relatively thin-walled member 26 with the relatively thick-walled tube 26 of metal having a much higher degree of pli# `ability than member 26. For instance, tube 25 maybe of lead, zinc or alloys thereof.

Thelining may be applied, in molten state, by the use of a suitable horizontal centrifuge, schematically represented at i I in Fig. 4.

The lining or core 25, which ispreferably bonded to pipe 26, extends into. contact with shoulders 30,- and-its bore 50 isof a diameter approximately equalv to the common diameter of bores I8, 22 and 29.. Further, bore- 50-1'is concentric with the outer peripheral faeebof pipe 26, it following that the total 'Wall'thick'nes's T offthe composite tube is equal at all points` along and around the full extentthereoiw-If the bore and other peripheral face of pipe 26 be not-"concentric, the thinner portions of the pipe wall arecom. plemented by correspondingly thicker-portions of tube 25.. n y Y Shoulders 30 prevent any longitudinal bodily shifting of core 25 should there be no bond between the pipe andl core or should a bond, originally established, be later ruptured. l

It will be seen that the long bore 501s smooth and true throughout its lengthrandis'riaxial allnement with bores I8, 22 and29. 1

Section yI4 is thus formed as a compositef'drill collar consisting of a relatively rigidoiiter shell 26 of strong material having a relatively` high modulus of elasticity and particularly well adapt- .ed to take high stresses. of tension and torque and having proper 'characteristics to lprovide threaded connections capable of sustaining great loads, and of a much less rigid inner, tubular core 25 of relatively weak, pliant metal which adds most appreciably tothe weight of the collar. The core ,is solely a weighting member and plays no connective or load-bearing function, so its weaker, softer characteristics are inno way detrimental, in fact the characteristic of softness is advantageous in .that 'it'enables the core to take the effects of the mud-laden circulating fluid better than does steel and the core thus represents a upon several circumstances.

protective lining for the bore-wall of the outer tube. On the other hand, the steel pipe 26, which `will take the abrasive wear incident to contact with the rough bore-wall much better than the core-material, protects the outer face of the core from auch wear.

But even more important than this, the relatively pliant core adds extra weight to the outer tube without appreciably adding to the stiffness and rigidity thereof. I therefore provide a very thick composite collar which is much more limber than would be a collar of `equal thickness made entirely of steel. Consequently, the bending stresses may be absorbed by the collar, proper, rather than being concentrated on the relatively thin coupling ends, asis the case where the bodyproper is as rigid as is the usual collar made of thick-walled steel.

With the sections all fabricated as described above, it will be seen that threaded boxes are provided at each end of each section, the boxes being fashioned in the-outer, steel pipe. Accordingly, the upper end of section I4 may be coupled to the drill stem as described above while the lower end of that section may be coupled to section Ida by coupling member I 5,which, as has been said, is similar to member 20. The lower box 26; is adapted to take the threaded pin 52 of drill I It is found in connection with ordinary drill collars, that the coupling members between drillcollar sections are most apt to fail, because there are thick, rigid sections at both sides thereof and both sections concentrate the `bending stresses at the common point of connection. It is therefore in connection with such intermediate couplings as member I5 and the mating boxes, that my invention has particular merit, though this statement is not at all to be considered as indicating that the merit is limited to this particular use.

Nowthe choice of core material will depend If it is desired to have a very heavy collar-,and the bore of the tube 26 is true with respect to its outer peripheral face, or if the drilling speed is to be relatively sloweven though the `bore of Vthe outer tube he not exactly true, a very'heavy`lv metal such as lead may be used, this metalfhalng a speciiic gravity of about 11.35 as against about 7.8 for the steel,

outer tube.

Or, of course, if less` weight is neededJ pliant metal oralloys havinglthe v-charafzzteris ti. ,s set forth above, lbut of less specic gravity than lead, may be used,

On the other hand, if the drilling speed isto be high and the bore of the outer tube is* out of true to any appreciable extent, it is preferable that the choice be otherwise'. The reason for this may be pointed out by reference to Fig. 5, wherein an exaggerated condition of eccentricity is represented. Steel tube 26 as having a much thicker wall at 55'than at the diametrically opposite point 56. `With the lnetal of core 25 applied as described above, it will be apparent that the thickness of the core at 5l is much greater than at 58. Consequently the added mass of the core-metal at the left side of axis A is much greater than at the right side, and if the specific gravity of the core material were different from that of the outer-tube-metal, the whole collar would be out of dynamic balance when the drill stern is rotated, with obviously undesirable vibratory and gyratory effects resultlng therefrom. This would be the case if the core material were lead.

So, under these circumstances, itis desirable to use a core metal having not only the above characteristics of pliability, but also a specific gravity the same, or as closely as practicable the same.

is here indicated having a specific gravity of 7.2 may be used in connection with certain alloys: Or if the `steel has a specific gravity of '7.8, there may be pro- Vvided an alloy of Zinc with a relatively small lead-content, the proportions of lzinc and lead -being such that the alloy has a specific gravity of 7.8. In this manner, dynamic balance will be assured.

1n Fig. c, A1 have shown avariation which I- have mentioned before, namely the use of plain tubing as the outer wall. Here, tubing 26" has no internal upsets, its ends, however, being provided with internal threads 28 to take, for instance, threaded pins 23 or 24'vof coupling members or I5. The opposed ends`30. of pins 23' and 24' may be utilized as' shoulders to perform the same function as ascribed to shoulders in Fig. 2.

. In Fig. 7, I have shown a situation where the end ofouter tube 26 is formed as an integral Din-end 65 instead of the box 28 of the form of Fig; 2. Here, a threaded pin 66 is provided on upset 21,this pin being adapted to take a sleevecoupling 61 for attachment to adjacent sections of drill collar or to other elements of the drilling string. Or, of course, a given drill collar section may have a pin at one end and a box at the other.4

In both Figs. 6 and 7, the associations vand l. re-used in the making of a new drill collar.

While I have shown and described a preferred embodiment of my invention, it'will be understood various changes mai7 be made without departing from the spirit and scope of the appended claims.

I claim: y

1. A composite drill collar embodying an outer torque transmission tube of steel and an inner tube of relatively pliant metal, the inner tube tightly iitting the.' bore of the outer tube and stopping short of the ends of the outer tube, and

an internal thread at each end of the outer tube beyond the ends of the inner tube. Y

2. A composite drill collar embodying an outer torque transmission tube of steel, a pair of longitudinally-spaced opposed annular shoulders projecting into the tube bore, and an inner tube of relatively pliant metal tightly fitting within the said bore and extending longitudinally from shoulder '6o shoulder, the diameter of the inner tube bore being at least as great as the diameters of the bores dened bythe annular shoulders.

3. A composite drill collar embodying a relatively rigid outer torque-transmission tube whose inner peripheral face is eccentric with relation to its outer peripheral face, and a relatively pliant inner tube of metal tightly tting the bore ofthe outer tube and varying circumferentially in wall thickness in Vsuch relation to the specified eccentricityof the peripheral faces of the outer tube that the aggregate wall-thickness ofV the composite collar is circumferentially uniform; the

material of the outer and inner tubes having substantially the same specific gravity.

4. A composite drill collar embodying a relatively rigid outer torque transmission tube and an inner tube of relatively pliant metal, the inner tube tightly tting the bore of the outer tube and stopping short of at least one end of the outer tube, and an internal thread at said one end of the outer tube beyond the associated end of the inner tube. A 5. In a drill stem, a pipe section, a threaded pin on the pipe section, a composite drill collar embodying a relatively rigid outer torque transvmission tube and an inner tube of relatively pliant metal, the inner tube tightly fitting the bere of the outer tube and stopping short oi.' at least one end of the outer tube, an internal thread at said one. end of the outer tube beyond the associated end of the inner tube; the threaded pin" tting said internal thread and the end of the pin presenting an annular shoulder adapted to contact the end of the inner tube of the composite collar at said one end of the collar.

ALBERT L. STONE. 

